Silver complex diffusion transfer process

ABSTRACT

A continuous tone transparency is produced from X-ray or radioactive radiation by means of the silver complex diffusion transfer process by exposing a light-sensitive material carrying a silver halide emulsion layer to a beam of such X-rays or radiation, treating the exposed layer with a photographic developing compound for 3-30 seconds with an aqueous developing solution having a pH between 10.5 and 11.5 at a temperature between 25* and 35*C, bringing the light-sensitive material in the presence of a silver halide complexing agent into contact with image-receiving material including a transparent hydrophobic film support and an image-receiving layer containing development nuclei for the complexed silver halide, maintaining the two materials in contact for a period of 10-60 seconds while at a temperature between 30* and 60*C, and finally separating the materials from one another. The exposure can be made directly to the beam of X-rays or radiation or, alternatively, a fluorescent intensifying screen can be associated with the light-sensitive material whereby a visible image is first formed in such screen by exposure to the X-rays or radiation and the light-sensitive material is exposed from such visible image.

lluite States atet 1 De lilacs [451 .luly 31, B973 1 SILVER COMPLEXDIFFUSION TRANSFER PROCESS [75] Inventor: Louis Maria De Haes, Edegem,

Belgium [73] Assignee: Ag1a-GevaertN.V., Mortsel,

Belgium [22] Filed: Aug. 3, 1971 [21] Appl. No.: 168,749

Related US. Application Data [63] Continuation of Ser. No. 714,467,March 20, 1968,

abandoned.

[52] 11.8. Cl. 250/65 F, 96/29 R, 96/82, 96/76 R [51] Int. Cl. G01n21/34 [58] Field of Search 96/29, 76; 252/62.l; 250/65 [56] ReferencesCited UNITED STATES PATENTS 2,887,379 /1959 Blake.... 96/82 3,185,8415/1965 Land..." 250/65 2,765,240 /1956 Land..... 117/34 3,351,46611/1967 Land 96/29 OTHER PUBLICATIONS Larmore Introduction toPhotographic Principles Prentice1-1all 1958 page 112-119 PrimaryExaminer-Norman G. Torchin Assistant Examiner.lohn L. GoodrowAttorney-William J. Daniel [57] ABSTRACT A continuous tone transparencyis produced from X-ray or radio-active radiation by means of the silvercomplex diffusion transfer process by exposing a lightsensitive materialcarrying a silver halide emulsion layer to a beam of such X-rays orradiation, treating the exposed layer with a photographic developingcompound for 330 seconds with an aqueous developing solution having a pHbetween 10.5 and 11.5 at a temperature between and C, bringing thelightsensitive material in the presence of a silver halide complexingagent into contact with image-receiving material including a transparenthydrophobic film support and an image-receiving layer containingdevelopment nuclei for the complexed silver halide, maintaining the twomaterials in contact for a period of 10-60 seconds while at atemperature between 30 and C, and finally separating the materials fromone another. The exposure can be made directly to the beam of X- rays orradiation or, alternatively, a fluorescent intensifying screen can beassociated with the light-sensitive material whereby a visible image isfirst formed in such screen by exposure to the X-rays or radiation andthe light-sensitive material is exposed from such visible image 5Claims, No Drawings SILVER COMPLEX DIFFUSION TRANSFER PROCESS This is acontinuation of Ser. No. 714,467, filed Mar. 20, 1968, now abandoned.

It is an object of the present invention to provide a method for quicklyproducing, according to silver complex diffusion transfer process, acontinuous tone transparency of an object exposed to a beam of X-rays orof a radio-active radiation. The darkest parts of the transparency thusobtained correspond with those parts of the object which absorb theradiation beam in the strongest way. Consequently, the transparency maybe considered as a positive copy of the object to be reproduced.

Another object of the present invention is to provide a method forobtaining such continuous tone transparencies with a high maximaldensity and a neutral image tone.

A further object of the present invention is to provide a method forobtaining such continuous tone transparencies which can be considered asbeing dry for all practical purposes immediately after the diffusiontransfer image has been formed and the light-sensitive and theimage-receiving materials have been separated from eaCh other.

Still another object of the present invention is to provide a method forobtaining two of such continuous tone transparencies at the same timeand from a single object-wise exposed light-sensitive material.

Further objects of the present invention will in part be obvious and inpart appear hereinafter.

The method of the invention comprises the consecutive steps of exposingan object to be reproduced to a beam of X-rays or of a radio-activeradiation, recording the objectwise modified beam either directly orindirectly on a light-sensitive photographic material comprising asilver halide emulsion layer, treating the lightsensitive materialcarrying the recorded latent image in the presence ofa developingcompound for 3 to 30 seconds with an aqueous alkaline processingcomposition having a pH between 10.5 and 11.5 and a temperature between25 and 35C, bringing the light-sensitive material in the presence of acomplexing agent for the silver halide into contact with animage-receiving material comprising a transparent hydrophobic filmsupport provided with an image-receiving layer comprising a substance orsubstances in order to form a silver containing image from the diffusingcomplexed silver halide, keeping the light-sensitive material and theimagereceiving material for to 60 seconds in contact with each otherwhilst being heated between 30 and 60C, and finally separating both thelight-sensitive material and the image-receiving material from eachother.

By proceeding in this way, it is possible to obtain in a very shorttime, mostly comprised between about 30 seconds and about 3 minutes, anexcellent and positive continuous tone transparency of an object exposedto a beam of X-rays or of a radioactive radiation. The method of thepresent invention possesses the further advantage that no extensive butrather only a compact processing unit is necessary and that the copiesobtained are dry whereby they can be stored immediately without firstdrying them. Consequently, the method of the present invention isparticularly suitable for being applied in cases wherein quickinformation of an X-ray or a radioactive radiation examination isnecessary, and this quick information often has to be obtained in littleideal working circumstances such as e.g. during a chirurgicalintervention, in war circumstances, in accident rooms to quicklydetermine the seriousness of a wounding, in industrial applications fortracing defects, and so on.

The light-sensitive silver halide emulsion for use in the method of thepresent invention is preferably a high sensitive emulsion layer. Silverbromide emulsion layers which contain minor amounts of silver iodide areparticularly suitable. The desirable high sensitivity of thelight-sensitive layer can be obtained in the usual way by physical andchemical ripening of the silver halide emulsion. The light-sensitivematerial can also spectrally be sensitized, especially when it isintended to record indirectly the object-wise modified radiation beam.Thus, in case of screen image photography, it should mostly besensitized ortho-chromatically.

The object-wise modified radiation beam may be recorded directly by thelight-sensitive material, but mostly is recorded indirectly.

This indirect recording may occur by first converting the oject-wisemodified radiation beam into a visible screen image which will berecorded on the lightsensitive material, in other words by the so-calledscreen image photography.

Preferably, however, the object-wise modified radiation beam issubstantially indirectly recorded in that it is for the greater partdetected by one or more fluorescent or luminescent intensifying orreinforcing screens in contact with the light-sensitive material and thefluorescent or luminescent image thus produced is recorded in the silverhalide emulsion layer in addition to the part of the radiation beam thathas been directly recorded. The sensitivity attained by processing thesilver halide emulsion layer thus exposed according to the method of thepresent invention may be from two to five times as high as that attainedby producing a negative image of the object by normal negativedevelopment. The said gain in sensitivity is evidently of greatimportance in that it enables a corresponding reduction of the dosageradiation on the object. Especially in medicine, where said objects arehuman beings, it is very important that said dosage be as small aspossible. According to the present invention, the highest sensitivity isattained by using two screens, one at either side of a light-sensitivematerial with a transparent support.

All the usual and generally known fluorescent or luminescentintensifying screens are suited for being used according to the latterembodiment of the present invention. As a matter of fact, the screenshould be chosen according to the characteristics of the lightsensitivematerial. A fluorescent or-luminescent intensifying screen can also bebuilt in the light-sensitive material by incorporating adaptedfluorescent or luminescent substances into at least one layer. Thislayer may be the emulsion layer itself. It is also possible toincorporate said substances into the support of the lightsensitivematerial. Frequently used and particularly suitable fluorescent orluminescent screens are among others calcium tungstate screens, bariumtungstate screens, zinc sulphide screens and leadand barium sulphatescreens.

By proceeding according to this embodiment with at least one fluorescentor luminescent intensifying screen in contact with the light-sensitivematerial, the silver halide content of the light-sensitive emulsionlayer need not be quite high. An amount per sq.m equivalent to l to 5 gof silver nitrate suffices in general. This is a further advantage overthe above described method for producing a negative image of the objectin a lightsensitive silver halide material wherein the latter shouldcontain per sq.m. mostly an amount of silver halide equivalent to aboutto about 45 g of silver nitrate.

When the object-wise modified beam is indirectly recorded, thesensitivity attained by proceeding according to the present method inmost cases can still be improved by incorporating a light-reflectingcompound, such as a white pigment, e.g., titanium dioxide and bariumsulphate, into at least one layer of the lightsensitive material,including the support, situated at the side of the silver halideemulsion layer opposite to that of the screen.

If it is a fluorescent or luminescent image including a screen imagewhich is recorded by the light-sensitive material, it is also possibleaccording to the present invention to produce at the same time twodiffusion transfer prints from one and the same object-wise exposedlight-sensitive material, on condition that the latter is provided witha light-sensitive layer on both sides of a transparent support. Later onan image-receiving material is pressed under about identicalcircumstances against either of both sides of the light-sensitivematerial so that after separation two diffusion transfer copies of aboutthe same quality are obtained.

Except in the case of screen image photography, the light-sensitivematerial is in most cases comprised in a usual cassette during therecording of the object-wise modified beam on the light-sensitivematerial in the first processing step of the method of the presentinvention. This is generally known to those skilled in the art. Variantsare also possible. Thus, the light-sensitive material can be containedin an evelope of a non-alkaliresistant synthetic product, for instancecellulose phthalate, which does not allow the visible light to passthrough but does allow X-rays and radio-active rays to pass through. Inthis way, the light-sensitive material can be stored and exposed to theobjectwise modified beam in day-light. ln contact with the aqueousalkaline composition for carrying out the diffusion transfer imageformation, the envelope of synthetic product desintegrates and thelight-sensitive material is set free so that it can be processed.

The support of the light-sensitive material for use in the method of thepresent invention may be any suitable and usual support, such as a papersupport, or a hydrophobic transparent support of a synthetic product,such as a cellulose triacetate support, a polyester support, preferablya biaxially stretched polyethylene terephthalate support, further apolystyrene support and so on. A transparent support, however, ispreferred and is even necessary for some embodiments such as the one forobtaining simultaneously two diffusion transfer copies from a singlelight-sensitive material and the one according to which also at thebackside of the light-sensitive photographic material a fluorescentintensifying screen is used. The support can first be provided with oneor more adhesive layers before the light-sensitive silver halideemulsion layer which in most cases is a gelatino silver halide emulsionlayer, is applied thereto. As the case may be, still one or more otherlayers may be applied before the emulsion layer is coated. Thelight-sensitive material can also be provided with a layer of awater-permeable hydrophilic colloid on top of the silver halide emulsionlayer. Ap-

plying such a top layer is generally known in the art of diffusiontransfer. In this connection, we can refer to the United Kingdom PatentSpecifications 1,052,022 filed Aug. 2, 1963, 1,054,252 filed Aug. 6,1963, to the published Dutch Patent Application 281,744 filed Aug. 3,1962 and to the United Kingdom Patent Specification 1,055,711 filed Jan.30, 1964 all by Gevaert Photo-Producten N.V. Besides the usual emulsioningredients, such as plasticizers, hardeners, emulsifying agents etc.,the light-sensitive silver halide emulsion layer and/or at least onewater-permeable layer in effective contact with the emulsion layer canalso contain ingredients which are necessary or of great importance forthe primary and/or the difiusion transfer image formation such asdeveloping substances, among others those listed hereinafter, toningagents, especially those listed further in the description, compoundswhich counteract the silver sludge deposition (antisludge agents) in theaqueous alkaline treating composition, etc.

For suitable compounds which counteract the silver sludge deposition inthe aqueous alkaline processing composition, we can refer among other tothe German Patent Specification 962,767 filed June 16, 1954 by Agfa AG,the US. Pat. No. 3,240,603 issued Mar. 15, 1966 of Horst Schiller,Herbert Grabhofer and Hans Ulrich, the Belgian Patent Specification677,090 filed Feb. 28, 1966 by Gevaert-Agfa N.V., the United KingdomPatent Specifications 940,169, 959,182 and 959,661 all filed July 27,1961 by Agfa AG and the published Dutch Patent Applications 66,14290filed Oct. 11, 1966, and 67,02133 filed Feb. 13, 1967 both byGevaert-Agfa N.V. A particularly suitable antisludge agent is3-heptadecyl-4-m-f1uorosulphonylphenyl-ureido-A -l,2,4-triazolin-5-thione.

The processing step which follows after the recording of the latentimage in the light-sensitive material is rather critical and the givenlimits should be considered very accurately in order to reach a highsensitivity for the method according to the present invention and at thesame time to obtain quickly a positive continuous tone transparency ofan optimal quality. These are the most important objects of the presentinvention. By an optimal continuous tone transparency is understood atransparency with a sufficient maximum density, a soft gradation and aneutral image tone.

This next processing step comprises, as indicated in the statement ofinvention, the treatment for 3 to 30 seconds of the light-sensitivematerial carrying the recorded latent image in the presence of adeveloping compound with an aqueous alkaline treating composition, whichhas a pH comprised between 10.5 and 1 1.5 and a temperature comprisedbetween 24 and 35C. The pH is preferably comprised between 10.9 and l1.3 and the temperature between 28 and 32C. In order to obtaincontinuous tone transparencies of the same quality, it is of importancethat the pH and the temperature of the aqueous alkaline processingcomposition and the period wherein the light-sensitive photographicsilver halide material is wetted with this aqueous alkaline composition,be kept as constant as possible.

This processing step can be carried out in different ways, for instanceby dipping the light-sensitive material into said aqueous alkalinecomposition, by conducting it at a constant speed through saidcomposition contained in a usual apparatus, or by wetting the soleemulsion side of the light-sensitive material with said composition bymeans of a kiss roller. In order to obtain a uniform diffusion transfercopy, it is of importance that the aqueous alkaline processingcomposition acts for about the same time upon each part of thelight-sensitive material.

The aqueous processing composition contains alkaline substancesnecessary to bring the pH at the desired value. The usual alkalinesubstances are sodium hydroxide, potassium hydroxide, lithium hydroxide,sodium carbonate and trisodium phosphate.

The developing compounds necessary for the development of thelight-sensitive material and also for the diffusion transfer imageformation may be present in at least one member of the light-sensitivematerial, the image-receiving material and the alkaline processingcomposition, but are preferably at least partly present in the latter.As regards the incorporation of developing substances into the materialsused (light-sensitive and image-receiving material), we can refer to theUnited Kingdom Patent Specification 1,012,476 filed Dec. 18, 1961 byGevaert Photo-Producten N.V. and to the published Dutch PatentApplications 279,797 filed June 15, 1962 and 281,744 filed Aug. 3, 1962both by Gevaert Photo-producten N.V., Photo- Producten the UnitedKingdom Patent Specifications 1,057,273 filed Feb. 3, 1964 by GevaertPhoto- Producten N.V. and 1,086,510 filed Dec. 16, 1964 by Gevaert-AgfaN.V. and to the Belgian Patent Specification 641,298 filed Dec. 16, 1963by Gevaert Photo- Producten N.V.

Particularly suitable developing substances for use in the method of thepresent invention are hydroquinone, 1-phenyl-3-pyrazolidinone andderivatives, paminophenol, pyrocathechol, p-amino-o-cresol,pamino-m-cresol, p-mono-methyl-aminophenol sulphate,p-dimethylaminophenol sulphate, pyrogallol and 2,4-diamino-phenol.Mostly two or more developing substances are used together. Particularlyfavourable results can be attained by using together hydroquinone andl-phenyl-3-pyrazolidinone or a derivative thereof in the aqueousalkaline processing composition, as the case may be together withp-monomethylaminophenol sulphate. The preferred concentration of thesedeveloping substances per liter of aqueous alkaline treating compositionis of about 9 to about 32 g of hydroquinone, of about 0.2 to about 5 gof l-phenyl-3- pyrazolidinone or a derivative therof, and of 0 to about10 g of p-monomethylaminophenol sulphate.

The aqueous composition comprises in most cases still other usualingredients such as conservatives for the developing substances,compounds liberating halide ions such as potassium bromide, compoundsfor improving the soft gradation in the low densities of the diffusiontransfer copy such as polyvinylpyrrolidone, anti-sludge agents such asthose identified above, toning agents for the diffusion transfer image,preferably those given hereinafter, and complexing agents for thenon-developed silver halide. Suitable complexing agents are among othersammonium thiosulphate and sodium thiosulphate. These two complexingagents are often used together. The anti-sludge agents are preferablysupplied by the aqueous alkaline processing composition, although inmany cases they can be present with favourable result in thelight-sensitive material as already stated above. In the processingcomposition they are in most cases supplied in concentrations of 20 to400 mg per litre, preferably in concentrations of to 250 mg per litre.

After the light-sensitive material has been treated with the aqueousalkaline composition as described above, it is brought into contact withan imagereceiving material in the presence of a complexing agent fornon-developed silver halide. This imagereceiving material is preferablydry at the moment that it is brought into contact with thelight-sensitive material, but it can also be wetted previously, e.g.with the same aqueous alkaline processing composition with which thelight-sensitive material was wetted. This wetting of the image-receivingmaterial can occur by conducting the image-receiving material accordingto the usual and generally known method together with thelight-sensitive material through the treating composition or by wettingherewith the image-receiving side of the image-receiving material bymeans of a kiss roller. The complexing agent for silver halide can bepresent in the aqueous alkaline processing composition, as alreadydescribed, and/or in the receiving material as will be describedhereinafter.

It is also possible to have present the image-receiving layer on top ofthe light-sensitive silver halide emulsion layer on a same transparentsupport, if necessary with a suitable separating layer between them.Hereby the steps of treating the light-sensitive material with thealkaline processing composition and of bringing it into contact with theimage-receiving material become reduced to a single step of treating themultilayer material with an aqueous alkaline processing composition inthe presence of a developing compound and a complexing agent for silverhalide.

The image-receiving material for use in the method of the presentinvention comprises a transparent hydrophobic film support provided withan image-receiving layer that comprises a substance or substances inorder to form a silver-containing image from the diffusing complexedsilver halide.

The hydrophobic transparent film support can be a polyester preferably abiaxially stretched polyester support, e.g. of polyethyleneterephthalate, a polybisphenol ester of an aliphatic and/oraromatic'dicarboxylic acid, a polyester of the polycarbonate type, etc.;it can also be prepared from a polymer of copolymer, such aspolystyrene, copoly[vinyl chloride/vinyl acetate] or of a hydrophobiccellulose ester such as cellulose triacetate.

The image-receiving layer is applied in the usual thickness to thetransparent film support, the latter mostly being provided with asubbing layer, from a dispersion of said substance or substances for thediffusion transfer image formation in an aqueous solution of a binder.Suitable binders are water-permeable hydrophilic colloids, such asgelatin and casein, occasionally mixed with a minor amount of a naturalor snythetic product, such as gum arabic, carboxymethylcellulose sodiumsalt and sodium alginate. It is also possible to apply severalimage-receiving layers to each other.

The following so-called development nuclei and ingredients which canform development nuclei are particularly suited as substance orsubstances to form a silver-containing image from the diffusingcomplexed silver halide; the sulphides of heavy metals, e.g. ofantimony, bismuth, cadmium, cobalt, lead, nickel, silver and zinc.Selenides, polysulphides, polyselenides, mercaptanes, tin(l1) halides,heavy metals or their salts and fogged silver halide are also suitablefor this purpose. The complex salts of lead sulphide and zinc sulphideare effective either in themselves or mixed with thioacetamide,dithiobiuret and dithio-oxamide. The concentration wherein these nucleior ingredients which form such nuclei are present in the image-receivinglayer is in most cases situated between about 0.002 and about 0.2 g per100 g of binding agent.

Besides the image-receiving layer, the imagereceiving material cancontain still other waterpermeable layers such as a protective layer, aseparating layer, etc. All these layers can occasionally be hardened inthe usual way. The image-receiving material may contain in at least oneof its water-permeable layers one or more compounds which take a part inthe diffusion transfer image formation. In particular can be mentioneddeveloping substances as those mentioned above, a complexing agent fornon-developed silver halide, such as ammonium thiosulphate (which at thesame time possesses a toning action), and sodium thiosulphate, as thecase may be in an additional amount to the complexing agent alreadypresent in the aqueous alkaline processing composition, anti-oxidizingagents, alkali-consuming substances, dyestuffs, toning agents,preferably those given hereinafter, and anti-sludge agents, such asthose referred to above. Incorporating the latter compounds into theimage-receiving material, of course, has only sense if theimage-receiving material is wetted with the alkaline processingcomposition before it is brought into contact with the lightsensitivematerial.

The presence of dyestuffs, especially yellow dyestuffs, in one of thewater-permeable layers of the image-receiving material or in the mass ofthe transparent support itself is sometimes useful for giving thediffusion transfer copy obtained a more neutral appearance.

As regards the toning agents having the same function of making for amore neutral appearance of the diffusion transfer copy, it is to benoted that those for use in the method of the invention in most casesdiffer from the usual toning agents for use in the diffusion transferprocess wherein the light-sensitive material is a less sensitive one, inmost cases a silver chloride material Preferably the toning agents arepresent in the image-receiving material but they can also be appliedsuccessfully to the light-sensitive material and/or to the alkalineprocessing composition as already stated above, especially to thealkaline processing composition. In the image-receiving material thetoning agents are in most cases applied in a concentration of about 20to about 500 mg, preferably in a concentration of about 50 to about 150mg per sq.m.

Hereinafter follows a list of toning agents with specific examples thathave proved to be particularly suitable in the process according to thepresent invention. 1. Heterocyclic nitrogen-containing thioxo compounds,preferably of the imidazolidine-Z-thione type such as l-ptolyl-Q-imidnzolidino-l hionc,

H: O NH 1-allyl-2'imidazolidine-thionc of the thiazolidineoroxazolidine-Z-thione type such as O HgC-H C (I): S

Hz C NH 5-methyl-2-oxazolidine-thione,

methyl-di-[(2-thio-thiazolidin-3-yl )-methyl -amine, and

of the perhydro-l ,3-oxazine-2-thione type and theperhydro-l,3-thiazine-2-thione type, such as and of thetetrazoline-S-thione type, such as i w HN N1-phenyl-2-tetraz0line-li-thione,

and

benzoxazoline-Q-thione,

, N/C Ha1-(p-(limcthylamino-phenyl)-4,4,6-trimethyl-3,4-di-hydro-2-(1H)-pyrimidlne-thione,

a-pheuyl-5-1uetl1ylin1iuo-1,3,4-tMadiazolldjne-Z-thione,

2. Thiuram sulphides, such as bis(dimethyllhiocnrbamoyl) sulphide,

and xanthogenates, such as mtnssium-ethyl-xauthate 3. Bis-oniumcompounds, such as l,1'-ol hylmlc-bis-[pyridlnium chloride]l,1Hetmmotlnylene-bis-[pyridinlum chloride],

l,l-deeumethylene-bis-[pyridinium bromide] and amides, e.g.

the condensation product of 9 to 10 moles of ethylene oxide withnonylphenol 5. Compounds such as aeeto-acetanilide, and

There are also some developing substances which at the same timefavourably influence the image tone of the diffusion transfer image,especially developing substances of the 0- or p-dihydroxybenzene typesuch as hydroquinone sulphonic acid sodium salthydroquinone-thiosulphonic acid potassium salt,

[HOQ-O-c: 0-0113 hydroquinone monoaeetate,

and

C II:

p-tcrt-hutyl-pyrocatechol,

p-aininophenol and salts 4-amino-o-cresol and salts l S 03-N82-1utlroxy-S-monomethyl-aininobeuzene-sulphonic acid sodium saltp-beuzylaminoplienol hydrochloride,

3-(p-liydroxyanilino)-propi0nitrilo,

2-amino-res0rcinol hydrochloride, an (1 Callsl-thyl-G-hydroxy-l.2,3-1-tetrahydroquiuoliue hydrochloride Thelight-sensitive material and the image-receiving material are kept incontact with each other for to 60 seconds whilst heating as uniform aspossible between 30 and 60C. This may occur by means of heated platesbetween which the light-sensitive material and the image-receivingmaterial are pressed against each other as uniformly as possible. Bythis pressure a better contact may be obtained between thelight-sensitive material and the image-receiving material whereby thesharpness of the diffusion transfer image is favourably influenced.Besides the diffusion transfer image formation is accelerated by thepressure and by the supplied heat.

In order to lower the salt concentration of the diffusion transfer copyobtained, avoiding thereby the risk of a visible crystallization ofthese salts, it is often advantageous to rinse the ontained diffusiontransfer copy before storing it, preferably in an aqueous mixture whichquickly evaporates from the rinsed copy so that the latter is quicklydry. Suitable aqueous mixtures are mixtures of water and a loweraliphatic alcohol, such as methanol and ethanol. 7

Finally, after a first diffusion transfer copy has been produced thelight-sensitive material can still be used for producing furtherdiffusion transfer copies by bringing the light-sensitive material inthe above described circumstances again and again into contact withfurther image-receiving materials and by separating it therefrom afteran optimal period of contact.

More particulars concerning the silver complex diffusion transferprocess in general and suitable equipment for carrying out said processcan be found in Progress in Photography Vol. 1; 1940-1950, pages 76, 77and Vol. 11, 1951-1954, pages 156-157; Vol. 111, 1955-1958, pages 24-26and the Patent Specifications mentioned therein. For suitable equipmentfor carrying out the process of the present invention, there may beespecially referred to the United Kingdom Patent Specification 852,838filed Oct. 3, 1957 by Gevaert Photo- Producten N.V. and to the UnitedKingdom Patent Specifications 1,060,572 filed Feb. 10, 1964 by GevaertPhoto-Producten N.V. and 1,077,355 filed Sept. 10, 1964 by Gevaert-AgfaN.V. and to the published Dutch Patent Application 65,09864 filed July29, 1965 by Gevaert-Agfa N.V.

Hereinafter follow some examples for illustrating the process of thepresent invention.

EXAMPLE 1 For preparing the light-sensitive material, a high sensitivegelatino silver bromo-iodide (3 moles percent iodide) emulsion with aratio of gelatin to silver nitrate of 1.5, was applied to agelatin-subbed cellulose triacetate support having a thickness of 0.1 mmin such a way, that per sq.m. an amount of silver halide equivalent to2.5 g of silver nitrate was present. After drying, an unhardened gelatinlayer was applied to the lightsensitve emulsion layer in a ratio of l gof gelatin per sq.m.

An image-receiving material was prepared by applying an image-receivinglayer to a gelatin-subbed cellulose triacetate support having athickness of 0.1 mm. This image-receiving layer was applied in a ratioof 1 litre per 10 sq.m. from the following coating composiuon:

water 825 ccs gelatin 41 g 0.2 by weight dispersion of nickel sulphidenuclei in a 10 aqueous solution of gelatin 41 ccs 1 solution in ethanolof bis(dimethyl-thiocarbamoyl) sulphide 82 cos 12.5 aqueous solution ofsaponine 4 ccs sodium thiosulphate-S-water 5 g 20 aqueous solution offormaldehyde 2 ccs The light-sensitive material was placed into a usualmetal cassette with a usual calcium tungstate fluorescent screen againstthe emulsion side. A sheet of black paper was applied to the backside ofthe light-sensitive material.

At the side of the fluorescent screen the lightsensitive material wasexposed to a skull phantom subjected to an X-ray radiation (distance 75cm 75 kV 64 mAs).

The image-wise exposed light-sensitive material was removed from thecassette together with the imagereceiving material described above, andconducted in the usual way through an aqueous alkaline processing liquidof the following composition distilled water 600 ccslphenyl-Ii-pyrazolidinone 1 g anhydrous sodium sulphite 75 8 sodiumhydroxide 8 hydroquinone 16 8 p-monomethylaminophenol sulphate gpotassium bromide 1 8 anhydrous sodium thiosulphate 50 g distilled xaterto 1000 (365 ethanol 200 1 solution of3-heptadecyl-4-ml,2,4-triazoline-5-thione in ethylene glycol monoethylether 20 CCS The pH of this treating liquid amounted to l 1.2 and theliquid was kept at 30C. The conduction of the materials through thisprocessmg composition proceeded in such a way that each part of thelight-sensitive material was wetted for about 7.5 seconds before thelight-sensitive material and the image-receiving material were pressedagainst each other between two rubber rollers in the usual way, whichwas the next processing step in the diffusion transfer image formation.

The sandwich of light-sensitive and image-receiving material in contactwith each other was then kept pressed for 30 seconds between two metalplates heated at 40C, whereafter the light-sensitive and theimage-receiving materials were separated from each other.

A positive copy of a good quality was obtained. This copy wassufficiently dry for examination purposes. It could be dipped for someseconds into a mixture of water and ethanol (50/50) in order to wash outthe major part of the absorbed salts. The minor amount of said mixturetaken up the copy quickly evaporated so that said positive copy verysoon was completely dry.

EXAMPLE 2 The process described in example 1 was repeated but instead ofusing only one fluorescent screen for the exposure, two screens wereused viz. one at either side of the light-sensitive material. The sheetof black paper at the backside of the light-senstive material wasomitted.

The exposure dose for the same distance and the same tension amounted toonly 20 mAs.

A same good result as described in example 1 was attained.

EXAMPLE 3 The process described in example 1 was repeated, but here thelight-sensitive silver halide emulsion layer and the gelatin layer ontop thereof were applied to a biaxially stretched polyethyleneterephthalate support provided in order with a polyethylene isophthalatelayer, a gelatin-cellulose nitrate layer and a lightreflecting titaniumdioxide layer. The latter was coated m a ratio of 30 g of titaniumdioxide per sq.m. from a composition prepared by thoroughly mixing 60 gof gelmm with 375 g of titanium dioxide and i000 ccs of water, and byadding per litre of the mixture thus obtained 20 cos of a l 1.7 percentaqueous solution of saponine apd cos of a 5 percent aqueous solution ofchromic a um.

The image-receiving layer too had another composition and was applied ina ratio of 1 litre per 12 sq.m from the following coating composition850 ccs of water The exposure dose for the same distance and the sametension amounted to only 32 mAs. The white pigment layer containing thetitanium dioxide particles was responsible therefor.

The positive copy obtained was of good quality and excelled in itsneutral image tone. Immediately after it had been formed it wassufficiently dry for examination purposes.

I claim:

1. Method for producing a continuous tone transparency according to thesilver complex diffusion transfer process, comprising the consecutivesteps of exposing an object to be reproduced to a beam of X-rays or of aradioactive radiation, recording the object-wise modified beam on alight-sensitive photographic material comprising a silver halideemulsion layer while said emulsion layer is arranged with one sidethereof in contact with at least one fluorescent or luminescentintensifying or reinforcing screen, said emulsion being a silver bromideemulsion containing a minor amount of silver iodide and having a silverhalide content equivalent to l to 5 grams of silver nitrate per squaremeter, treating the light-sensitive material carrying the recordedlatent image in the presence of a photographic developing compound for 3to 30 seconds with an aqueous alkaline processing composition having apH between 10.5 and l 1.5 and a temperature between 25 and 35C, bringingthe light-sensitive material in the presence of a complexing agent forsilver halide into contact with an image-receiving material comprising atransparent hydrophobic film support provided with an image-receivinglayer containing development nuclei for forming a silver-containingimage from the diffusing complexed silver halide and a toning agent in aconcentration of about 20-500 mg/sq.m., keeping the lightsensitivematerial and the image-receiving material for l0 to 60 seconds incontact with each other whilst heating between 30 and 60C to form thedifiusion transfer image in said receiving material, and finallyseparating both the light-sensitive material and the imagereceivingmaterial from each other.

2. Method according to claim 1, wherein the toning agent isbis(dimethylthiocarbamoyl)sulphide.

3. Method according to claim 1, wherein an antisludge agent is presentin the aqueous alkaline processing composition.

4. Method according to claim 3, wherein the anti sludge agent is3-heptadecyl-4-m-fluorosulphonylphenyl-ureido-A l,2,4-triazoline-5-thione.

5. Method according to claim 1 wherein said photographic materialcomprises a layer other than said emulsion layer containing a whitepigment and situated on the side of said emulsion opposite from saidscreen. *9 t t 4 ll

2. Method according to claim 1, wherein the toning agent isbis(dimethylthiocarbamoyl)sulphide.
 3. Method according to claim 1,wherein an anti-sludge agent is present in the aqueous alkalineprocessing composition.
 4. Method according to claim 3, wherein theanti-sludge agent is 3-heptadecyl-4-m-fluorosulphonyl-phenyl-ureido-Delta 2-1,2,4-triazoline-5-thione.
 5. Method according to claim 1wherein said photographic material comprises a layer other than saidemulsion layer containing a white pigment and situated on the side ofsaid emulsion opposite from said screen.